The Hague, Netherlands (CNN) -- U.S. President Barack Obama on Tuesday hailed the achievements of the Nuclear Security Summit here, including some countries' agreements to give their highly enriched uranium to the United States for degrading.
"We've seen such steps as Belgium and Italy completing the removal of their excess supplies of highly enriched uranium and plutonium so that those supplied can be eliminated," he said at a joint news conference with Mark Rutte, the Prime Minister of the Netherlands.
And dozens of other nations have agreed to take steps to improve nuclear security in their own countries and to support global efforts, the U.S. President said. "So what's been valuable about this summit is that it has not just been talk, it's been action."
Hours after Obama landed Monday in The Netherlands for the summit, the White House announced a deal to dispose of huge quantities of nuclear material from Japan.
Obama credited the heads of state who participated in the effort, "as well as the extraordinary work of foreign ministers and sherpas and others who have helped to move this process forward."
The United States is doing its part, too, by installing more radiation detection equipment at ports and other transit sites to thwart would-be smugglers of nuclear materials; by developing guidelines to strengthen cybersecurity at nuclear power plants; and by pursuing production of an isotope used in medicine that does not require weapons-usable materials, he said.
But more work is to be done "to fully secure all nuclear and radiological material ... so that it can no longer pose a risk to our citizens," he added.
"Given the catastrophic consequences of even a single attack, we cannot be complacent."
He noted that Ukraine agreed at the first such summit, in 2010, to remove its highly enriched uranium from its nuclear fuel sites. "Had that not happened, those dangerous nuclear materials would still be there now, and the difficult situation we are dealing with in Ukraine today would involve yet another level of concern."
Before the next such summit, to be held in 2016 in Chicago, "we have to set very clearly what are the actionable items that we've already identified that we know can get done if we have the political will to do them, and let's go ahead and get them done," he said.
Tuesday's session marked the third such gathering of world leaders since Obama helped launched the initiative in 2009.
According to a report issued last year by the Center for Nonproliferation Studies, the United States will spend at least $179 billion over the nine fiscal years of 2010-2018 on its nuclear arsenal.
CNN's Tom Watkins and Jason Hanna contributed to this report